Dynamical origin of Dimorphos from fast spinning Didymos
Dynamical origin of Dimorphos from fast spinning Didymos
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DOI：
10.1016/j.icarus.2023.115428
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发表时间：
2023-01
期刊：
影响因子：
3.2
通讯作者：
G. Madeira;S. Charnoz;R. Hyodo
中科院分区：
文献类型：
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作者：
G. Madeira;S. Charnoz;R. Hyodo
Didymos是一颗双近地小行星。它是DART和HERA太空任务的目标。主天体Didymos的旋转速度接近于它预计会脱落质量的旋转速度。第二天体Dimorphos是一颗140米长的卫星，它在大约12小时内绕着第一天体运行。在这里，我们调查了Dimorphos的可能起源。使用环/卫星相互作用的一维模型，我们研究了从Didymos表面丢失的物质的演变，并在其赤道沉积成环。我们发现，由于粘性扩展，环扩展到Didymos的罗氏极限之外，形成小卫星。一小部分质量将形成迪莫斯和一组接近洛希极限的物体，而环的大部分质量福尔斯落回迪莫斯。为了匹配今天的迪莫斯的性质，必须沉积在环中的总质量约为迪莫斯质量的25%。可能有一小部分物质在环和Didymos表面之间旅行了几次。该模型产生的轨道类似于Didymos潮汐参数k 2/Q≤ 1 0− 5时观测到的轨道。如果环沉积时间尺度较长（≥ 1 0 2年）（因此物质通量较小），则Dimorphos可能是不规则形状的，因为它是由相似大小的小卫星碰撞形成的。然而，由于小行星的快速自旋，预计Didymos的顶部形状将实现，这将导致短沉积时间尺度（100 yr）。在这种情况下，卫星将由在罗氏极限处逐渐增生的物质形成，从而形成由尺寸在米量级的小块构成的椭圆形Dimorphos，这显然与DART使命获得的Dimorphos最近的图像一致。
Didymos is a binary near-Earth asteroid. It is the target of the DART and HERA space missions. The primary body, Didymos, rotates close to the spin at which it is expected to shed mass. The secondary body, Dimorphos, is a 140 meters moon that orbits the primary body in about 12 h. Here we investigate the possible origin of Dimorphos. Using 1D models of ring/satellite interactions, we study the evolution of material lost from Didymos’ surface and deposited as a ring at its equator. We find that due to viscous spreading, the ring spreads outside the Didymos’ Roche limit forming moonlets. A fraction of the mass will form Dimorphos and a set of objects near the Roche limit, while most of the ring’s mass falls back on Didymos. To match the properties of today’s Dimorphos, the total mass that must be deposited in the ring is about 25% of Didymos’ mass. It is possible that a fraction of the material travelled several times between the ring and the surface of Didymos. The models produce an orbit similar to that observed for a Didymos tidal parameter k 2/Q≤ 1 0− 5. If the ring deposition timescale is long (≥ 1 0 2 yr)(so the material flux is small) Dimorphos could be irregularly shaped as it forms from the collision of similar-sized satellitesimals. However, the top-shape of Didymos is expected to be achieved due to a fast spin-up of the asteroid, which would result in a short deposition timescale (≲ yr). In that case, the satellite would form from progressively accreting material at the Roche Limit, resulting in an ellipsoidal Dimorphos constructed of small pieces with sizes of the order of meters, which is apparently in agreement with the recent images of Dimorphos obtained by DART mission.